1. Field of the Invention
The present invention relates to fastening devices for joining a sheet to a member at an angle from the sheet. More specifically the present invention relates to a joint for joining a flangeless tube sheet of an aluminum heat exchanger to a perpendicular bracket for securing the heat exchanger thereto.
2. Prior Art
The present invention provides for a strong, secure and inexpensive method for joining an aluminum tube sheet without flanges to a structural support member located perpendicular to the end thereof. Previous tube sheets were manufactured from steel such that flanges were provided at the ends thereof and could be bolted directly to supporting brackets. Other methods of joining previous tube sheets included lancing the tube sheet to form a series of parallel spaced portions and then deforming these portions alternately in opposite directions to form a cavity in which a screw could be inserted such that the threads would engage these portions. It has been found that this particular lancing arrangement is not effective when used with aluminum due to the characteristics of the aluminum and the screw threads becoming dislodged.
The advent of aluminum heat exchangers with aluminum tubes and fins and the newly developed ultrasonic soldering techniques has made it necessary to develop aluminum tube sheets in order to have an entirely aluminum heat exchanger. The utilization of an aluminum tube sheet has required that new joining methods be utilized to mount the heat exchanger within the appropriate unit. The typical heat exchanger is comprised of a plurality of joined hairpin tubes having a multiplicity of fins mounted onto the hairpins such that a continuous fluid circuit is formed when the hairpins are joined together with return bends. This type of heat exchanger typically referred to as a plate fin coil has a tube sheet mounted on each end thereof to secure the fins therebetween. The refrigerant typically flows through the hairpins and return bends such that heat is transferred between the refrigerant and the air in contact with the fins and tubes.